the effect of basil seed gum and xanthan on the physical and rheological characteristics of low fat mayonnaise

introduction: an emulsion is made of dispersed particles through the continuous phase, while not dissolving happens between two phases. mayonnaise is oil-in- water emulsion (james and dakin, 1962), as one of the most sauces used in the world. it has a mild odor and taste, creamy to pale yellow color and a ph in the range of 3.6- 4.0, which does not exceed 4.1 (iranian national standard, no 2454). emulsion products are naturally instable. different factors such as temperature, particles size, stirring, mechanical movements, constituents’ concentration, presence or absence of stabilizers and thickeners may affect the emulsion stability (david, 1999). ocimum basilicum l., known as basil (or ‘‘reyhan” in iran), is a common herb plant grown in iran. soaking in water, basil seeds become gelatinous. the high mucilage content of basil seeds can make it a novel source of edible gum (razavi et al., 2008). the objective of this paper was to investigate the effect of basil seed gum as well as xanthan as fat replacers on some physical and rheological properties of low fat mayonnaise. materials and methods: emulsion stability determination: mayonnaise samples were centrifuged at 5000 rpm for 30 minutes. emulsion stability (es) was then determined using the following relation (worrasinchai s et al., 2006): stability index= (total volume/ volume of emulsion remaining)100. particle size measurement: particle size distribution of low-fat mayonnaise samples was determined using laser light diffraction technique (fritsch analysette 22, germany). rheological measurements: a rotational viscometer (visco 88, malvern, uk) equipped with a thermal circulator was used to measure the steady shear rheological properties of samples at the shear range of 14-300 s-1 and constant temperature of 25 oc. power law, bingham, casson, and herschel-bulkley models were fitted on the experimental data and the rheological parameters of these models were determined using slidewrite plus-bar graph software (1983, advanced graphics software, inc, usa). image processing: a scanner was used to capture the samples’ image and the scanner resolution was set to 300 dpi. 7g sample was placed onto a plate and then 152×210 pixel parts was cut from the obtained image. all images were stored in jpeg format for further analysis. the clemex image processing software (clemex vision professional, pe4, canada) was used to determine the color parameters (l*, a* and b*). results and discussion: steady shear flow behavior: the results showed that all samples are classified rheologically as non-newtonian shear thinning fluids. according to r2 values, power law was considered as the best rheological model to describe the flow behavior of samples. the maximum and the minimum consistency coefficients of power law model were observed for the formulation containing 0.75% xanthan gum and 0.45% basil seed gum, respectively. in this study, the apparent viscosity of mayonnaise (in shear rate 42 s-1) raised with increasing gum concentration that this increase in samples 4 and 5 were not significant (p>0.01). the highest apparent viscosity was observed in sample 3 that was prepared with a concentration 0.75% of xanthan gum, while the lowest viscosity was related to sample 4 that was contained of 0.45% basil seed gum. with increasing gum concentration, bingham viscosity of the samples increased, but this increase in the samples (1, 7, 8) and (2, 6, 9) was not significant (p> 0.01). yield stress values of herschel-bulkley (τh), bingham (τb) and casson (τc) models raised with the increasing of gum concentration. highest yield stress value was related to mayonnaise containing 0.45% xanthan gum and the lowest yield stress value related to mayonnaise prepared with 0.45% basil seed gum. particle size distribution: particle size distribution of mayonnaise at concentration of 0.6 % xanthan gum, basil seed gum and mixture of xanthan- basil seed gum had mono-modal particle size distribution. emulsion stability: among samples, formulations of 1, 2, 3, 8, and 9 were quite stable and there was no instability (two-phase state). higher stability in emulsions containing xanthan gum was probably due to higher viscosity of this gum compared to basil seed gum. color: the best color was observed in sample 6. in this study, with increasing concentration of gum in three samples (1, 2, 3), the amount of l* decreased, it means that the brightness of the product was reduced while in samples containing a mixture of gums (xanthan- basil seed gum), increasing the gum concentration resulted in an increase in l* parameter.